End formation of a round tube into a square section having small corner radii

Expansion and reduction are the two common end forming processes for tubes. In the tube end expansion process using a square punch, it is difficult to obtain a small corner radii due to the stretching of the tube around the punch corners. The wall thickness around the corners is small when compared to the side wall. Hence, a tube having a poor square look is formed. In this study, a 2-stage end expansion of a round tube end into a square section having an improved square look i.e. small corner radii and increase in wall thickness around corners is developed. In the 1st stage, the tube end is flared into a cone shape using a 30° conical die by axial compression. In the 2nd stage, the conical end of the tube is drawn through a taper square die using a conical bottom square punch, and a near square section is formed. A 15% ironing ratio is applied during the drawing process to flatten the side wall of the square. Experimental and FEM simulation were performed to evaluate and to verify the forming process. Although the height of the square section increases when the punch stroke at the 1st stage is increased. However, this increase is limited by the buckling of the pipe at the circular section of the thick blank tube. Since the conical end is drawn into a square section having different radial lengths, the bottom of the square section is uneven. The uneven bottom end is trimmed off in the later process. A square section having a maximum height of 32 mm after trimming is successfully obtained from the experiment for the punch stroke, S = 44 mm using an API 5 L tube.     

A probabilistic crystal plasticity model for modeling grain shape effects based on slip geometry

A new statistical theory is introduced that takes into account the coupling between grain size, shape and crystallographic texture during deformation of polycrystalline microstructures. A “grain size orientation distribution function” (GSODF) is used to encode the probability density of finding a grain size D along a direction (given by unit vector n) in grains with orientation g. The GSODF is sampled from the input microstructure and is represented in a finite element mesh. During elastoplastic deformation, the evolution of grain size D (in direction θ) and the orientation g is tracked by directly updating the GSODF probabilities using a Lagrangian probability update scheme. The effect of grain shape (e.g. in high aspect ratio grains) is modeled by including the apparent grain size as seen by various different active slip systems in the grain within the constitutive law for the slip system resistance. The prediction of texture and strains achieved by the statistical approach is compared to Taylor aggregate and finite element deformation analysis of a planar polycrystalline microstructure. The role of grain shape and size in determining plastic response is investigated and a new adaptive GSODF model for modeling microstructures with multimodal grain shapes is proposed.     

The Effect of a Nanosize TiO<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript> Layer on the Performance of an Organic Solar Cell

This work studies the role of a cathodic TiO_x buffer layer in operation of a photovoltaic organic solar cell (OSC) based on a photoactive layer with a bulk heterojunction. Using a liquid solution to obtain a TiO_x layer is of current interest for simplification of process technologies of successive formation of OSC layers. It is found that the optimum thickness of the TiO_x layer is 10 nm; at this thickness, the efficiency of the OSC reaches the value of 4.36%. The effect of air oxygen on the OSC samples is studied and it is found that samples with a TiO_x buffer layer undergo degradation to a lesser extent as compared to the samples with no such layer. The effect of oxygen on operation of the photovoltaic device is discussed.     

Ar/O2 gas pressure dependences of a pulsed zirconium arc and extracted ion characteristics

A pulsed dc zirconium arc discharge is generated in an argon diluted oxygen gas by separating a pin electrode as an anode from the cathode. The arc is transiently generated, and its life time is approximately 3 ms for a series resistance of 1 Ω and a dc output of 33 V. The life is prolonged and the plasma becomes stable with increasing the arc current. A target with a diameter of 100 mm is set at 150 mm from the arc source, and is immersed in the plasma. A pulse voltage is applied to the target to extract ions from the plasma. The ion current is not detected after approximately 8 ms since the plasma initiation. When the plasma is generated in oxygen without argon, the plasma generation time is scattered, and the plasma is unstable. An ion density is estimated from the temporal behavior of the target voltage in the recovery region after the pulse voltage. The ion density at the target is approximately 2.5 × 10¹⁵ m^− 3 at a mixed gas pressure of 1.9 Pa, which corresponds to the plasma density of 1.1 × 10¹⁷ m^− 3 under an assumption of electron temperature of 1 eV.     

The perturbation dimension for describing rough surfaces

We define global and local “perturbations” of roughness profiles, considered as rectifiable or non rectifiable curves. The method consists in measuring classical roughness parameters in τ — windows of various sizes. When τ tends to zero a characteristic scaling exponent is evaluated. This exponent is related to the “perturbation dimension” d. In rectifiable cases d is an integer. Otherwise, d is a real number. As a practical application, we characterize the roughness evolution of a shot-blasted surface as a function of the abrasive particule size.     

The investigation of a novel approach in the simulation of the trap levels effect on the conduction in a GaAs P+νN+ diode

A numerical simulation using C⁺⁺ language, allowing the store of big size information (presented as (X × Y × Z) matrix) is realized, and a theoretical modelling of the charges transport in the semiconductor devices made in materials presenting a significant concentration of impurities whose energy levels are deep is implemented. The results are validated on a semi-insulating gallium arsenide (SI-GaAs) PIN structure. The numerical simulation is made by the resolution of the phenomenological transport's equations by adopting a new approach permitting to study the conduction phenomena through all the structure. From the 3D modelling, the variation of the potential profile, the free carriers and the space charge distributions, and the electrical field inside the structure are simulated. The effects of the traps are taken into account through the mechanisms of recombination and storage of a significant space charge, where the influence of the presence of these levels on the above factors is seen. Through this work a physical model intended for the study of the influence of the trap levels on the potential and the free carrier density distributions for weak lifetime semiconductors, more particularly on semi-insulating GaAs is introduced. Taking into account the trap centres is essential for a good comprehension and explanation of the transport phenomena. The present study consists to do a simulation and a modelisation of structures based on materials presenting a deep and a trap centres. A trapping model based on a combined numerical method Gummel and Newton is adopted to reduce both the run time and to reach convergence in the process when working not with one junction but with two.     

Hot deformation behavior of KFC copper alloy during compression at elevated temperatures

1 Introduction Along with the recent development in the semiconductor industries, precipitation-hardenable alloy copper strips with high electrical conductivity and strength, as well as excellent heat resistance, were commonly used as a leadframe materia…     

Study on the indentation size effect in CaF2: Dislocation structure and hardness

In this study nanoindentations have been performed on a cleaved surface of a CaF₂ single crystal and the dislocation structure has been investigated by the etch pit technique using atomic force microscopy. The deformation during indentation is first purely elastic until dislocations are created observable in a pop-in in the load displacement data, as well as in a dislocation rosette around the indentation. After pop-in a relatively high hardness is observed, which gradually decreases, until at 3 μm a nearly constant hardness is found. By using sequential polishing, etching and imaging, the dislocation structure underneath indentations with indentation depths of 300 nm and 110 nm (load: 5 mN, 1 mN) is quantified. The dislocation density and radial distribution of dislocation density depend on the indentation depth, where a smaller indentation depth leads to a higher dislocation density, which is in qualitative agreement with the observed increase in hardness.     

A dislocation model for the minimum grain size obtainable by milling

Primary among the processing techniques that are now available for synthesizing bulk nanocrystalline materials is ball milling, which produces nanostructures by the structural decomposition of large-grained structures as the result of severe cyclic deformation. It is well-documented that during milling, the grain size decreases with milling time, reaching a minimum grain size, d_min, which is a characteristic of each metal. In this paper, a dislocation model that predicts the value of d_min as a function of material parameters, such as hardness, melting temperature, and stacking fault energy, has been developed. The model is based on the concept that d_min is governed by a balance between the hardening rate introduced by dislocation generation and the recovery rate arising from dislocation annihilation and recombination. It is demonstrated that the model provides possible explanations for several recent observations regarding the characteristics of d_min.     

Aufkohlung von Chrom-Nickel-Eisen-Stählen in der Kohlenstoffpackung

Carburization of chromium nickel steels in a carbon bed Annealing the samples in carbon powder is a simple method for testing the carburization behaviour of heat resistant CrNiFe steels. It is shown that according to the thermodynamic conditions during this test a very thin layer of Cr₂O₃ is formed on the surface of the samples in the temperature range 900° to 1050°C. This layer virtually prevents carburization. Above 1050°C. The oxide layer is transformed to a carbide and carburization of the alloy can take place without restraint. However, the influence of temperature on carburization as described may not apply to service conditions, in particular, carburization may also occur if the oxide layer is thermodynamically stable but porous and fissured. Upon carburization carbon is diffusing into the alloy and reacting with chromium and iron under formation of the carbides M₇C₃ in an outer zone and M₂₃C₆ in an inner zone. The penetration of these zones is also determined by the solubility of carbon in the carburized region. By a high nickel content of the alloy the carbon solubility is diminished and therefore the rate of carburization is retarded. This influence of the nickel content also shows under service conditions.     

Roughness prediction on laser polished surfaces

The paper presents a methodology to predict the surface topography on laser polished surfaces. The method is based on the thermal field prediction generated by the laser. The thermal field is obtained through the differential equation of heat transfer by conduction. The prediction of the resulting topography is based on the filtering of the spatial frequency spectrum of the initial topography which is obtained by FFT analysis. Once the temperature field is obtained, a critical frequency is calculated and a low-pass filter is applied to cut the frequencies higher than the critical one. The resulting surface is reconstructed using the remaining frequencies. The methodology has been tested on a DIN 1.2379 tool steel and the experimental validation shows a relatively good agreement between the predicted and measured values of mean roughness (R_a) and mean roughness depth (R_z), with errors lower than 15% in all the cases.     

嗜酸兼性异养菌Acidiphilium sp.DX1-1的分离、特征及其浸矿行为(英文)

研究了一株源自江西德兴铜矿矿区的中温嗜酸兼性异养菌Acidiphilium sp.DX1-1的分离、鉴定、特征及其浸矿行为。菌株Acidiphilium sp.DX1-1为短杆状革兰氏阴性菌,最适合的生长温度为30℃,最适合的生长pH约为3.5。该菌株具有广泛的底物利用特性,可以利用有机物进行异养生长并在细胞内积累聚羟基丁酸酯,也可以利用单质硫、三价铁等无机物进行自养生长。系统发育分析表明DX1-1属于Acidiphilium属,与Acidiphilium cryptum and Acidiphilium multivorum的同源性大于99%。在铁闪锌矿生物浸出过程中,Acidiphilium sp.DX1-1表现出极强的浸矿能力,其作用不仅仅是之前报道的作为其他自养嗜酸浸矿细菌的辅助者。在初始pH3.5时,DX1-1能够在一个月内单独地浸出铁闪锌矿中40%的锌。该浸出率高于它与A.ferrooxidans混合以及A.ferrooxidans单独浸出铁闪锌矿(初始pH均为2.0)的浸出率。     

A revision of the Fe-Ni phase diagram at low temperatures (<400 °C)

The low-temperature Fe-Ni phase diagram was assessed experimentally by investigating Fe-Ni regions of meteorites using high resolution analytical electron microscopy techniques. The present phase diagram differs from the available experimental phase diagram based on observations of meteorite structure, but it is consistent with the available theoretical diagram in that α/Ni₃Fe equilibrium was found at low temperatures. The a phase containing 3.6 wt.% Ni is in local equilibrium with the γ′ (Ni₃Fe) phase containing 65.5 wt.% Ni, while the γ′' (FeNi) phase is present as a metastable phase. The new phase diagram incorporates a monotectoid reaction (γ₁ → α + γ₂, where (γ₁ is a paramagnetic fcc austenite, a is a bcc ferrite, and γ₂ is a ferromagnetic fcc austenite) at about 400 °C, a eutectoid reaction (γ₂ → α + γ′) at about 345 °C, and a miscibility gap associated with a spinodal region at low temperatures. The miscibility gap is located between 9.0 and 51.5 wt. % Ni at ～200 °C. The new low-temperature Fe-Ni phase diagram is consistent with all the phases observed in the metallic regions of meteorites.     

A study of EDM and ECM/ECM-lapping complex machining technology

EDM (electrodischarge machining) and ECM (electrochemical machining)/ECM-lapping complex machining is investigated in this paper. First, EDM shaping and ECM finishing technology are investigated. These processes are carried out in sequence on the same machine tool with the same electrode (copper) and the same machining liquid (water). Two types of EDM and ECM complex machining are investigated. One is with a formed electrode, and the other is with simple-shape electrode scanning. The complex machining with electrode scanning is applied to produce small and various-shaped components without making a formed electrode. The EDM surface of 1 μm Ra is improved to 0.2 μm Ra by applying ECM. Second, in order to get a smoother surface, a new EDM and ECM-lapping complex machining technology is developed. The surface roughness of a machined hole is improved to 0.07 μm Ra by applying 2 min of ECM lapping. The surface finishing of a hole shape is demonstrated with the complex machining technology.     

The dependence of the Eshelby model predictions on the microstructure of metal matrix composites

The present work discusses an important modification to the classical Eshelby model, as used on metal matrix composites. It is shown that including the reinforcement orientation distribution in the model improves its agreement with experimental data, taken on 6061Al–15 vol.%SiC_w composites. In particular, a density of hydrostatic, deviatoric as well as axial and radial matrix stress as a function of the angle with respect to the extrusion axis is calculated. It is found that the orientation distribution density is such that the whiskers oriented near to the extrusion axis contribute significantly to the transverse (i.e. radial) deviatoric matrix stress. It is also found that a dramatic increase (400%) of the matrix deviatoric stress occurs as a function of the amount of oriented reinforcement, while the hydrostatic matrix stress has a range of variation of ±40%. Finally, the influence of the equivalent Eshelby temperature of mixing ΔT_E is discussed to show that (a) the residual stress (RS) depends linearly on ΔT_E; and (b) the deviatoric RS is more sensitive to its variation. An estimation of ΔT_E is recommended, by means of mechanical properties and RS measurements in order to avoid incongruence.     

High rate of copper electrodeposition from the hexafluorosilicate bath

A high-rate copper electrodeposition performed from a hexafluorosilicate bath is presented in this article. It is shown that the current density for electrodeposition ranges from 1 to 30 A dm^− 2 and the optimal suggested current density is 15 A dm^− 2 or a rate of 200 μm h^- 1. High plating rate is due to a higher mass transport through the hexafluorosilicate media when compared to a conventional sulphate-based bath. The microstructure, texture and mean grain size of the 30 μm-thick films plated from the additive free bath and the bath containing 10^− 3 mol dm^− 3 thiourea and 500 ppm Cl⁻ is studied with respect to the applied current density. Copper plated from the bath without additives has a macrocrystalline structure with preferable 110 texture and mean grain size of 65-85 nm, while thiourea produces a microsmooth surface and 111 texture with grain size of 40-70 nm.     

Measurement of grain boundary triple line energy in copper

Recent studies have demonstrated that grain boundary triple junctions are crystal defects with specific thermodynamic and kinetic properties. In this study we address the energy of triple lines. Previously, a geometrical model was proposed to determine the grain boundary line tension. The current study introduces a thermodynamically correct approach which allows direct and precise measurement of the triple line energy. The experimental technique utilizes the measurement of the surface topography of a crystal in the vicinity of a triple junction by atomic force microscopy. The grain boundary triple line tension ${\gamma }_{\mathit{TP}}^l$ of a random triple line in a copper tricrystal was measured to be 6.3 ± 2.8 × 10^?9 J m^–1.     

Unusual electron transport in Heusler-type Fe2VAl compound

The electrical resistivity of D0₃-type (Fe_1−xV_x)₃Al shows an anomalous temperature dependence characterized by a resistance maximum near the Curie point and a negative resistivity slope at higher temperatures up to 1000 K and above. In particular, the Heusler-type Fe₂VAl compound is found to be in a marginally magnetic state and to exhibit a semiconductor-like behavior with the resistivity reaching 3000 μΩ cm at 2 K, in spite of the presence of a clear Fermi edge as revealed in valence-band photoemission spectra. A substantial mass enhancement deduced from electronic specific-heat measurements suggests that Fe₂VAl is a possible candidate for a 3d heavy-fermion system. According to electronic structure calculations, Fe₂VAl is a nonmagnetic semimetal with a narrow pseudogap at the Fermi level. The unusual electron transport is mainly interpreted in terms of the effect of strong spin fluctuations, in addition to the existence of very low carrier concentrations.